The present invention relates to delayed-action thermal relays, and particularly to delayed-action thermal relays comprising a bimetallic element and a heating element composed of a material having a positive temperature coefficient (PTC).
As is known, single-phase induction or asynchronous electrical motors require special means for overcoming starting obstacles, particularly under load, and then entering into normal running conditions. The starting problem has been solved with various devices one of which provides the use of an additional motor starting winding which is disconnected after the motor has been started. To achieve this result, a relay with normally closed contacts is used which opens after a certain delay.
While the invention will be described as applicable to a relay as defined above and for the purpose indicated above, it should be understood that use in single-phase induction motors (examples of which are compressors for refrigerators and the like) does not exhaust other possibilities of application of such relays, said relays being able to be used effectively in any other application where there is need for a delayed actuation of the relay, i.e. in all circuits that require a certain time delay between actuation and response.
It should be noted furthermore that, while the invention is described with reference to contacts that are normally closed, the device as described can be readily modified to obtain a delayed-action relay with contacts that are normally open as needed for other applications.